Aircraft passenger seating comfort currently ranges from a single mechanical adjustment for economy seating to lavish suites with electrical actuators, lumbar adjustments, massage, lighting and many other comforts. For electronically controlled passenger comforts, there are two common system architectures, referred to as “single unit” and “distributed control unit.” Single unit architecture uses a single enclosure that houses all electronics used by the passenger. The collection of electronics is often referred to as a “suite,” and some or all of the suite may be housed within the actual passenger seat. All electrical actuators, lights, lumbar communication, in-flight entertainment (IFE) communications, and so on, are controlled via a single electronics box. One variation of this architecture houses the power supply in one enclosure and the control electronics in another enclosure.
Such architecture can be cost effective, for example, in applications that require only a few actuators or input output/output devices (e.g., lights). However, as the complexity of the system grows, the wiring in the passenger suite may need to be run back to the control electronics box, which is typically located under the passenger seat. The wiring harnesses can get quite complex and run tens of feet throughout the suite. To add to the complexity, for serviceability, harness disconnects are needed to enable removal of the seat and other components of the suite. The more wire connections that are needed throughout the suite, the larger the size of the electrical disconnects, which increases the weight of the control system. The increased weight can reduce the fuel efficiency of the aircraft, thereby increasing operating costs.
Distributed control unit architecture improves on single unit architecture by using multiple electronics boxes in a distributed controller area network (CAN), which often uses a commination protocol such as CANopen. There is a single master controller box that may include a power supply, or the power supply may be housed in a different enclosure. This single controller communicates using a CAN physical layer to any number of electronic nodes to control actuators, lighting and all other electrical functions of the passenger suite. Each node in the network has its own unique programmed address.
The distributed control unit architecture has a number of advantages over the single unit architecture approach. For example, electronics are distributed at the location they are needed without long runs of multiple wires. Also, only a single cable with power and separate communications wires are required between nodes, which reduces harness complexity and reduces system weight making the aircraft more fuel efficient. Moreover, the system can be easily expanded to include more nodes with only the CAN bus load being a limit. The distributed control unit architecture is further advantageous because the CAN physical layer handles the communications details.
The distributed control unit architecture, however, also has several drawbacks. First, each node is required to have a unique address. While there are several techniques for addressing nodes, including firmware addresses, DIP switch selection, rotary switch selection, and unique resistors values, most of these methods require the user to “program” an address for each node. The resistor technique, for example, sets an address for each node based on unique resistor values either on the node electronics or included in the CAN harness. Second, the bus end node is required to have a line termination resistor. The termination resistor causes some challenges regarding how the end node gets terminated, for example whether the node is user selected or whether it is incorporated in the CAN harness. Third, aviation requires the use of an MTh-spec cable. The cable that is required to run the power and CAN to each node is not a standard cable. The power leads are typically run as one twisted pair and the CAN is run as its own impedance-controlled pair. Fourth, CAN uses a square wave which has inherent odd harmonics making it more difficult to pass the stringent Aerospace regulatory requirements. Further, any special addressing technics must be included. Combining the power and CAN into one cable is typically a special-order item for an aircraft.